1. Field of the Invention
The present invention relates to an ink-jet recording process making use of so-called plain paper to which a special coating is not applied, and particularly to recording paper comprising neutral or alkaline paper with an excellent long-term shelf stability and permitting the formation of clear images and an ink-jet recording process making use of such recording paper.
The present invention also relates to recording paper permitting the formation of images excellent in water resistance and an ink-jet recording process making use of such recording paper.
This invention further relates to an ink-jet recording process making use of widely-usable recording paper which exhibits excellent properties even as toner-transfer paper suitable for use in electrophotographic recording systems and permits the formation of clear images even in ink-jet recording.
The term "neutral or alkaline paper" used in the present invention means a paper which is made so as to make the water extracted pH not less than 6 and without using aluminum sulfate as possible.
2. Related Background Art
Ink-jet recording systems have attracted attention because of ready attainment of high-speed, high-density and full-color recording. Such exclusive coated paper sheets as disclosed in, for example, Japanese Patent Application Laid-Open Nos. 59-35977 and 1-135682 have been used in such ink-jet recording systems.
Meanwhile, in the fields of black-and-white recording and business color recording, there has been demand for development of recording paper low in price and widely usable, in particular, recording paper usable in common as toner-transfer paper (paper for PPC) for copying machines and the like making use of an electrophotographic recording system, which are in common use in offices at present.
Problems involved in ink-jet recording making use of paper for PPC are the following two points:
(1) ink absorptivity is poor, so that when a great amount of an ink is applied to the paper, the drying and fixing of the ink are delayed (if an object comes into contact with a recording surface in the state that the ink is neither fixed nor dried, the image formed is impaired); and
(2) an ink spreads along fibers of the paper at the time the ink is absorbed in a paper layer, so that feathering of dots occurs to a great extent, and the peripheries of the dots hence become jagged and blurred, resulting in failure of the provision of clear characters and images.
A further problem involved in the ink-jet recording making use of the paper for PPC is that images formed are poor in water resistance, so that they run out and become illegible when they come into contact with waterdrops, or get wet with water.
Water-based inks comprising an aqueous solvent and a water-soluble dye have heretofore been used in ink-jet recording systems. Therefore, the use of a hardly water-soluble dye for the purpose of improving the water resistance of the resulting images offers problems that clogging due to deposition of the dye on the tip of a nozzle of an ink-jet recording head tends to occur, and the dye in the ink aggregates and precipitates if the ink is not used for a long period of time.
As a method for solving these contrary problems to each other, may be mentioned a method wherein a dye which is present in the form of a water-soluble salt (for example, ammonium salt) in an ink, but insolubilized (for example, counter ions being substituted by H.sup.+ ions by deammoniation to form an insoluble matter) on the surface of paper applied is used.
Examples of such dyes include ammonium salts of dyes disclosed in, for example, U.S. Pat. No. 5,053,495.
Meanwhile, in recent years, occasions to use neutral or alkaline paper in place of the conventional acid paper have increased due to problems of the shelf stability of paper and the like. Neutral or alkaline toner-transfer paper sheets excellent in electrophotographic recordability are disclosed in Japanese Patent Application Laid-Open Nos. 51-13244 and 59-162561.
Recording on neutral or alkaline paper for PPC making use of the above-described water-resistant dye offers a further problem that sufficient water resistance can not be imparted to the resulting image compared with the case of the conventional acid paper.
As described above, there has not yet been obtained under the circumstances any ink-jet recording process which permits the formation of images clear and excellent in water resistance on all the paper sheets for PPC including neutral or alkaline paper.